cGMP-dependent protein kinase phosphorylates and inactivates RhoA

Small GTPase Rho and cGMP/cGMP-dependent protein kinase (cGK) pathways exer t opposing effects in specific systems such as vascular contraction and gro wth. However, the direct interaction between these pathways has remained el usive. We demonstrate that cGK phosphorylates RhoA in vitro at Ser188, the same residue phosphorylated by cAMP-dependent protein kinase. In HeLa cells transfected with constitutively active cGK (C-cGK), stress fiber formation induced by lysophosphatidic acid or V14RhoA was blocked. By contrast, C-cG K failed to inhibit stress fiber formation in cells transfected with mutant RhoA with substitution of Ser188 to Ala. C-cGK did not affect actin reorga nization induced by Rad or Rho-associated kinase, one of the effecters for RhoA. Furthermore, C-cGK expression inhibited the membrane translocation of RhoA. Collectively, our findings suggest that cGK phosphorylates RhoA at S er188 and inactivates RhoA signaling. The physiological relevance of the di rect interaction between RhoA and cGK awaits further investigation. (C) 200 1 Academic Press.